Ch19 Stars formation

Question 1

Star formation birth of a star

Answer 1

• interstellar dust cloud collapse under gravity.
• GPE is converted into ke, KE increase and the fore also temperature increases.
• when temperature reach 19 million K, this high temperature is required to overcome the repulsive electrostatic force of the nuclei.
  -hydrogen nuclei fuse into helium.
• radiation and gas pressure = gravity
• and a star is born

Question 2

Evolution of a star similar to the sun

Answer 2

Main sequence:
The star will be fusing hydrogen nuclei into helium.
The radiation pressure balances the gravitational force.
Eventually the hydrogen will run out, the star will collapse under gravity ( cuz there is no more radiation pressure).
The temperature increases even more
As the core is hotter, the outer layer of the star will expand and form a red giant.

Question 3

Red giant

Answer 3

The outer layer has expanded and cooled off.
Red giant will fuse helium into heavier elements.
It will eventually run out of helium, the star will collapse once again and gravity will win.
The star will form a planetary nebula and then it will form a white dwarf.

Question 4

White dwarf

Answer 4

• Characteristics of a white dwarf:
  Very high density.
  Small volume.
• in a white dwarf, what’s opposing the gravitational force is electron degeneracy pressure.
  Electron degeneracy pressure: it’s when electrons can not occupy the same energy level, they exert pressure to oppose the gravitational force.
• a star will end its life cycle as a white dwarf only if it’s below chandrasekah limit - 1.4 solar masses.

Question 5

Evolution of massive star

Answer 5

The star will be fusing hydrogen nuclei into helium.
The radiation pressure balances the gravitational force.
Eventually the hydrogen will run out, the star will collapse under gravity ( cuz there is no more radiation pressure).
The temperature increases even more
As the core is hotter, the outer layer of the star will expand and form a red super giant.

Question 6

Super red giant

Answer 6

Will fuse helium into heavier elements and those heavier elements will fuse into even heavier elements all the way up to iron, eventually the fuel will run out.
- slightly smaller star will turn into a neutron star after the gravitational collapse.
- larger star will form a black hole.

Question 7

Neutron star

Answer 7

Neutron star characteristics:
- very high density Small
- small volume
- very strong gravitational field

Question 8

Black hole

Answer 8

Black hole characteristics:
- its mass has collapsed into singularity; infinite density and an extremely strong gravitational field.